Add test for GetAttachments method with no attachment

Introduced a new test case to check `GetAttachments` when no attachments are present in the message object. Removed the redundant `TestMsg_GetAttachments` function to simplify the test suite.

msg_test.go

@@ -3276,6 +3276,16 @@ func TestMsg_GetAttachments(t *testing.T) {
 				messageBuf.String())
 		}
 	})
+	t.Run("GetAttachments with no attachment", func(t *testing.T) {
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		attachments := message.GetAttachments()
+		if len(attachments) != 0 {
+			t.Fatalf("GetAttachments: expected 1 attachment, got: %d", len(attachments))
+		}
+	})
 }
 
 // checkAddrHeader verifies the correctness of an AddrHeader in a Msg based on the provided criteria.
@@ -3488,53 +3498,6 @@ func checkGenHeader(t *testing.T, message *Msg, header Header, fn string, field,
 		}
 	}
 
-// TestMsg_GetAttachments tests the Msg.GetAttachments method
-
-	func TestMsg_GetAttachments(t *testing.T) {
-		tests := []struct {
-			name  string
-			files []string
-		}{
-			{"File: README.md", []string{"README.md"}},
-			{"File: doc.go", []string{"doc.go"}},
-			{"File: README.md and doc.go", []string{"README.md", "doc.go"}},
-			{"File: nonexisting", nil},
-		}
-		m := NewMsg()
-		for _, tt := range tests {
-			t.Run(tt.name, func(t *testing.T) {
-				for _, f := range tt.files {
-					m.AttachFile(f, WithFileName(f), nil)
-				}
-				if len(m.attachments) != len(tt.files) {
-					t.Errorf("AttachFile() failed. Number of attachments expected: %d, got: %d", len(tt.files),
-						len(m.attachments))
-					return
-				}
-				ff := m.GetAttachments()
-				if len(m.attachments) != len(ff) {
-					t.Errorf("GetAttachments() failed. Number of attachments expected: %d, got: %d", len(m.attachments),
-						len(ff))
-					return
-				}
-				var fn []string
-				for _, f := range ff {
-					fn = append(fn, f.Name)
-				}
-				sort.Strings(fn)
-				sort.Strings(tt.files)
-				for i, f := range tt.files {
-					if f != fn[i] {
-						t.Errorf("GetAttachments() failed. Attachment name expected: %s, got: %s", f,
-							fn[i])
-						return
-					}
-				}
-				m.Reset()
-			})
-		}
-	}
-
 // TestMsg_SetAttachments tests the Msg.GetAttachments method
 
 	func TestMsg_SetAttachments(t *testing.T) {